In 3GPP (3rd Generation Partnership Project), the standardization of LTE-Advanced (LTE-A) is in progress, as a fourth-generation mobile communication system to realize communication of further increased speed and increased volume from LTE (Long Term Evolution), which is an enhanced standard of the third-generation mobile communication system.
In LTE, MIMO (Multi Input Multi Output) techniques are under study as radio communication techniques to improve spectral efficiency (see, for example, non-patent literature 1). In MIMO techniques, a plurality of transmitting/receiving antennas are provided in the transmitter/receiver, so that different information sequences are space-division-multiplexed over the same frequency and the same time, and transmitted from a plurality of transmitting antennas. On the other hand, on the receiver side, taking advantage of the fact that fading variation is produced between the transmitting/receiving antennas, the information sequences that have been transmitted in the same frequency and the same time are separated and detected.
Also, in MIMO techniques, single-user MIMO (SU-MIMO) to transmit varying information sequences to a single user, and multiple-user MIMO (MU-MIMO) to transmit varying information sequences to a plurality of users, are defined. In downlink MU-MIMO transmission, varying information sequences for a plurality of user terminals are transmitted in the same frequency and the same time, from a plurality of transmitting antennas of a radio base station. In this way, in MU-MIMO transmission, it is possible to increase the number of user terminals to multiplex over the same radio resources (frequency and time), so that it is possible to improve the efficiency of use of radio resources.